Modeling The process of creating 3D Objects Polygon Modeling NURBS Modeling Subdivision Surfaces

Pipeline

Modeling In A Studio Pipeline In a studio environment, sculptors create maquettes to work out the shape of 3D models. This process is especially useful during character development to define the character shape before CG modeling begins.

Surface Normals A surface normal is a 3D vector that is perpendicular to a surface. Surface normals are used extensively during lighting calculations. During modeling surface normals can be modified or “flipped” which can cause problems further down the pipeline.

Plans & Production Drawings Production drawings and schematics are used as guides during modeling. In some cases the art director has a clear picture of how they want a model to look. If they have supplied production art, the modeling artist can work directly from the artwork.

Level Of Detail During the modeling process it is important to be aware of what the final output will be for the model. This includes how detailed the model needs to be for the production. A model used in a video game production will have much less detail that a model that will be used in a feature film.

Plan of Attack It is important to have a plan of attack when modeling. This generally includes deciding what type of modeling approach you are going to use and what modeling tools you are going to need. Especially for more detailed models, planning ahead can prevent you from redoing work over and over.

Polygon Primitives Maya gives the user a starting point with a number of primitive polygon models. These are the primitive polygon models available in Maya.

Valence Vertex Valence is defined as the number of edges that meet at a vertex. All vertices of a cube are have a valence of 3 All vertices of this object have a valence of 4

Polygon Components Edge Face Vertices Vertex – a point at the corner of a polygon Edge – a line connecting 2 vertices of a polygon Face – a surface created from 3 or more vertices Edge Face Vertices

Polygon Modeling Vertex Faces In addition to saving all the vertex information for a polygon shape, Maya stores the vertex information for each individual face. This can be especially useful during texturing.

Extrusions One common method of modeling polygons is by extruding faces to build geometry. This process involves selecting a polygon face and “pushing” the face outward in the direction of the surface normal to create new geometry.

Booleans Boolean operations create new geometry based on the relationship of two or more objects that have overlapping geometry. After a Boolean operation has been applied to two objects a new set of geometry is created. Boolean operations can create unclean geometry which can cause problems during rigging and lighting. B A

Booleans A Union B B Difference A A Difference B A Intersect B

Polygon Modeling One advantage of polygon modeling is the that the final model is one piece of geometry. This is especially useful for character animation due to the fact that a character setup artist can apply deformations to the entire model without worrying about seams.

Subdivision In order to given a polygon model more detail it is sometimes necessary to subdivide faces to add more surface detail. This process generally is used to refine a rough shape into a more detailed smoother surface. In Maya the polygon subdivide face tool creates a more detailed mesh without attempting to smooth the model. The polygon smooth tool adds more detail and smoothes the polygon model using the Catmull-Clark subdivision scheme.

Subdivision

Catmull-Clark Subdivision Scheme The smooth operation in Maya applies the Catmull-Clark Subdivision scheme to polygon models. When the Catmull-Clark subdivision scheme is applied to a polygon mesh a face point is created in the center of all faces, and an edge point is placed at the center of all edges. The Catmull-Clark subdivision scheme produces only quadrilaterals which is extremely useful when texturing..

Alternative Subdivision Schemes

Doo-Sabin Subdivision Scheme The Doo-Sabin subdivision scheme produces only valence 4 vertices.

Bevel Polygon models by definition have straight edges. In order to create realistic objects, modeling artist often have to smooth the corners or bevel polygon models. Beveling a polygon model adds detail to the sides of a object in order to create a rounded edge.

Bevel